He was supposed to kill her... instead he awakened her powers. He gave her his blood and in exchange she gave him a taste of hers. With that simple taste he had bound himself to her forever, as a servant and protector. Together they fight the Shinma, sending them back to the dark where they can no longer prey on humans... where they too will go some day.

She is Miyu of the Vampire Clan and he is Larva, once the leader of the Occident Shinma, now the glad servant of the young Miyu. They are bound together, once by accident the second by choise, but whether or not they are lovers...